GEOLOGICAL SURVEY CIRCULAR 773
Stratigraphic Test Well, Nantucket Island, Massachusetts Stratigraphic Test Well, Nantucket Island, Massachusetts
By D. W. Folger, J. C. Hathaway, R. A. Christopher, P. C. Valentine, and C. W. Poag
GEOLOGICAL SURVEY CIRCULAR 773
Description of Triassic(?) basalt and Upper Cretaceous to Pleistocene sediments recovered from 514 meters of test coring
1978 United States Department off the Interior CECIL D. ANDRUS, Secretary
Geological Survey W. A. Radlinski, Acting Director
Library of Congress catalog-card No. 78-600008
Free on application to Branch of Distribution, U.S. Geological Survey 1200 South Eads Street, Arlington, Ma. 22202 CONTENTS
Page Page Abstract ______. 1 Results Continued. Introduction ______. 1 Stratigraphy Continued Purpose ______-__. 1 Paleontology Continued Setting ______. 2 Pliocene or Miocene 15 Previous work ______3 Eocene ______. 16 Acknowledgments ______. 4 Paleocene ______. 16 Methods ______. 5 Borehole 6001 ______. 16 Results ______6 Pleistocene ______16 Stratigraphy ______6 Eocene ______17 General lithology ______6 Upper Cretaceous _. 17 Upper zone ______6 Porosity and permeability _. 18 Middle zone ______7 Discussion ______. 18 Lower zone ____ 8 Regional stratigraphy ______. 18 Saprolite and basalt 8 Regional structure ______22 Paleontology ______15 Hydrology . 23 Coskata well _____ 15 Summary ______. 26 Pleistocene ___. 15 References cited ______26
ILLUSTRATIONS
Page FIGURE 1. Index map of Nantucket Island and the surrounding area _ 2 2. Cross section showing structure of part of Continental Shelf south and west of Nantucket ____ _- 4 3. Columnar section of borehole 6001 ______- 6 4-6. Diagrams showing variations for the following chemical compo nents in the basalt and saprolite zones of borehole 6001: 4. Chemical elements and minerals ______14 5. TiC-2 and P205 ______15 6. Mn02 and CaO ______15 7. Stratigraphic sections showing regional correlation of Nantucket boreholes with other holes drilled in the Atlantic Coastal Plain to the west and south ______19 8. Section from New Jersey to Georges Bank showing environment of deposition of sediments ______21 9. Map showing gravity anomalies in Nantucket region ___ _ 23 10. Seismic reflection profile through Great Round Shoal Channel and Nantucket Sound ______24 11. Graph comparing salinity of interstitial water with electrical conductivity and lithology in borehole 6001 ______25
TABLES
Page TABLE 1. Partial chemical and X-ray modal analyses of volcanic rock and saprolite ______9 2. Porosity and permeability analyses ______18
III Stratigraphic Test Well, Nantucket Island, Massachusetts
By D. W. Folger, J. C. Hathaway, R. A. Christopher, P. C. Valentine, and C. W. Poag
ABSTRACT local generation of petroleum hydrocarbons in this shoreward area of the continental margin is unlikely. The U.S. Geological Survey, in cooperation with the Freshwater or low-salinity brackish water was Massachusetts Water Resources Commission and the found in sediments far below the depth predicted by Nantucket Conservation Foundation, continuously cored the Ghyben-Herzberg principle. These interstitial 514 m of sediment and volcanic rock in a Stratigraphic waters are probably relict ground water emplaced and water-quality test. during times of low sea level during the Pleistocene. Stratified sediments were divided texturally into three zones: the upper zone (0-128 m) contains mostly coarse sand and gravel; the middle zone (128-349 m) INTRODUCTION contains mostly silty clay and a few beds of sand and silt; and the lower zone (349-457 m) contains soft, PURPOSE unconsolidated, clayey sand. Below the lower zone, a In 1975, the U.S. Geological Survey (USGS), saprolite, composed mostly of clay, grades abruptly downward at 470 m into partially altered basalt that in cooperation with the Massachusetts Water extends to the bottom of the hole at 514 m. Resources Commission, planned to drill a 122-m Fossils are sparse throughout the cores, but Pleisto hole near the geographic center of Nantucket cene, Eocene, and Upper Cretaceous assemblages were Island to assess the total thickness of fresh identified. On the basis of limited foraminifer and water in the sediments. Calculations based on ostracode assemblages, Pleistocene deposits are in the Ghyben-Herzberg principle predicted a zone ferred to extend to a depth of about 85 m. A Lower Eocene section 25 m thick is defined on the basis of of freshwater 120-150 m thick (Kohout and palynomorph and dinoflagellate assemblages. (How others, 1977). This principle is the theory of ever, samples from a water well drilled in 1933, 10 hydrostatic equilibrium between freshwater km to the north, contain Pliocene and Miocene, early and more dense seawater in a coastal aquifer; Eocene, and Pal eocene foraminifers.) Upper Cretaceous it states that for each meter of ground-water beds, inferred to extend from 128 to 349 m, are iden tified mostly on the basis of pollen and spores. The elevation above sea level, the freshwater lens oldest datable fossiliferous sample at 345 m is early- will depress the saltwater interface about 40 m to-middle Cenomanian in age. below sea level. The USGS later proposed to Samples found below 345 m are barren of indigenous deepen the test to about 500 m, the approximate fossils and are assigned an Albian Age on the basis depth of a prominent acoustic reflector (Oldale, of electric log correlations. Paleontologic evidence sug gests that the Pleistocene section was deposited under 1969), which was assumed to be basement. The nearshore marine conditions, the Tertiary section un primary objective of the additional drilling was der open-shelf marine conditions, and most of the to obtain new Stratigraphic information near Upper Cretaceous section under nonmarine conditions. the shoreward margin of the Georges Bank The unstratified clay that makes up the saprolite basin. Seismic reflection and refraction surveys was probably formed by subaerial weathering of basalt similar to that which underlies the saprolite. Chemical by oil companies and by the USGS have been evidence suggests that the basalt was probably de carried out for several years in the region of posited as a series of flows. The oldest K-Ar date ob Georges Bank, where leasing of tracts and ex tained in the basalt was 183±8 m.y. (Early Jurassic); ploratory drilling are imminent. however, because of alteration, this probably repre The nearest pre-Pleistocene sedimentary sents a minimum age. strata exposed on land are Tertiary and Cre Lignites and coal in the Upper Cretaceous section are of low rank and, on the basis of their thermal im taceous clay and sand that crop out at Gay maturity, have probably never been buried deeply; thus, Head, Martha's Vineyard (fig. 1). However, MASSACHUSETTS BAY 4I°25'- NANTUCKET SOUND Great Point COSKATA BOREHOLE ( T.D. 102m)
Sankaty Head 41° 15'-
USGS BOREHOLE NO. 6001 (T.D. 514m)
70°00'
USGS BOREHOLE NO. 6016
USGS BOREHOLE NO. 6018 © and COST G1 STRATIGRAPHIC TEST
0 10 70° 00
FIGURE 1. Index map of Nantucket Island and surrounding area showing location of Nantucket stratigraphic test well (USGS borehole No. 6001) and other boreholes in the region. T.D. shows total depth of some of the boreholes. they are dislocated and highly folded and the coast of Cape Cod, Mass., on the eastern faulted, apparently from loading or "bulldoz Continental Shelf of the United States. It has ing" by glacial ice (Kaye, 1964), and they do a maximum elevation of only 33 m (Folger not provide a clear picture of the stratigraphy. Hill), and encompasses a total area of 132 km2. The Nantucket test-well site is located farther Exposed surficial sediments are mostly gla seaward from Martha's Vineyard, and it pro cial sand, gravel, and some clay (Richards, vided an opportunity to gain data where sedi 1962; Woodworth, 1934). These deposits are ments are thicker, closer to the basin center, part of the Ronkonkoma-Vineyard-Nantucket and presumably less affected by ice movements. moraine and its outwash plain that extends Furthermore, penetrating the sedimentary sec eastward to form part of Georges Bank (Pratt tion and identifying basement would be useful and Schlee, 1969). Controversy has surrounded in the interpretation of geophysical data col the age of shelly deposits underlying the sand lected to assess the resource potential of the and gravel at Sankaty Head (fig. 1), but most area. evidence available suggests that they are also of Pleistocene age (Richards, 1962; Gustavson, SETTING 1976). Nantucket Island is about 25 km long, as The well site (borehole 6001) is at lat much as 10 km wide, and lies 40 km south of 41°15/54.9// N. and long 70°02'16.72" W. near the geographic center of the island on land School student, and examined for microfossil owned by the Nantucket Conservation Founda content with the help of J. A. Cushman. On the tion, which, because of its interest in island basis of Foraminifera that he discovered in the water resource evaluation, kindly granted the fine-textured sediments, he assigned them a USGS permission to drill. The site was con Tertiary age. This work, remarkable for a high veniently located 60 m from Milestone Road, the school student, remained unpublished until now. main highway between Nantucket and Sias- The Coskata samples, which had been saved by conset (fig. 1), in a long linear depression Mr. Barrett, provided for us a Tertiary section known as Madequecham Valley that was prob that is mostly absent in the USGS borehole. ably eroded by a proglacial melt-water stream. Geophysical investgiations of the island to Ground surface elevation at the site is 10.9 m our knowledge have been sparse. Weston Geo above mean sea level. physical Co. conducted a refraction seismic and resistivity survey in 1966 (Massachusetts PREVIOUS WORK Water Resources Commission, written com Discussions concerning sediments of Nan mun.). One refraction line was long enough to tucket date back to Desor (1849) who suggested reach a high velocity (5.7 km/s) refractor at that fossils exposed at the base of cliffs at -509 m near the western end of the island. A Sankaty Head were Tertiary in age. In subse shorter line laid out along Milestone Road re quent work, this conclusion was hotly contested vealed two refracting horizons less than 46 m and a Pleistocene age for them was established deep close to the location of the USGS hole. (Merrill, 1896; Cushman, 1906; Richards, Oldale (1969) shot several refraction lines 1962) ; thus, most work on the geology of the along the beaches, but none was long enough to island has concerned its glacial evolution reach refractors with velocities in excess of (Shaler, 1889; Woodworth, 1934). However, 2.8 km/s. He did, however, compile all available extensive study of Tertiary and Cretaceous ex data in the Cape Cod, Martha's Vineyard, and posures on Martha's Vineyard at Gay Head, Nantucket area to construct a depth-to-base contiguous shores, and in pits located inland ment map. Though he had only the one site laid the basis for conjecture concerning the from Weston's unreversed line at which higher subsurface stratigraphy of Nantucket (Wood- velocity material was penetrated, his prediction worth, 1934; Kaye, 1964, 1972). of basement depth at the USGS borehole of Fourteen deep boreholes drilled on lower -500 m was within a few meters of the depth Cape Cod penetrated as much as 137 m of gla at which basalt was penetrated. cial clastic deposits and 172 m of bedrock com A deep CDP (common depth point) seismic posed of schist and granite (Koteff and Cotton, line (No. 5) was shot by the research vessel 1962; Oldale, 1976). Sediments of Tertiary age Gulf Seal, operated by Digicon Geophysical, (Eocene) were recovered in three holes drilled Inc., for the USGS Outer Continental Shelf near Provincetown, at the northern tip of Cape Resource Assessment Program, 20 km west of Cod (Zeigler and others, 1960). A hole has re Nantucket (Grow and Schlee, 1976). There, cently been drilled on Martha's Vineyard to a sediments overlying basement thicken from less total depth of 262.2 m; the core contains a con than 1 km nearshore to 8 km offshore beneath densed but similar stratigraphic section to that the Continental Slope. Figure 2 shows the proc penetrated on Nantucket (Raymond E. Hall, essed record and our interpretation of seismic USGS, written commun., 1977). line No. 5. West of Nantucket, the line appears On Nantucket, a water well was drilled in to cross several subsurfurce basins that may be 1933 using a manually operated cable-tool rig down-faulted. These have been interpreted on at Coskata, about 10 km north of USGS bore the basis of previous work to be Triassic or hole No. 6001 (fig. 1). No freshwater was re Jurassic grabens (Grow and Schlee, 1976, map covered, but the hole penetrated 44 m of sand 2; Ballard and Uchupi, 1975; Ballard and Sor- and gravel overlying 58 m of silt and clay. ensen, 1968; Uchupi and Emery, 1967; Uchupi, Cuttings from the hole were assembled in 1936 1968). by Walter Barrett, then a Nantucket High On the basis of magnetic data, Nantucket NW SHOT POINT NUMBER SE 600 700 800
EXPLANATION Q, Quaternary T, Tertiary K, Cretaceous J, Jurassic 1, Triassic M, Multiple
70°
LOCATION MAP
FIGURE 2. Cross section of part of Continental Shelf showing processed record and interpretation of USGS seis mic line No. 5 (CDP) south and west of Nantucket. Mi, M2, and M3 are interpreted as multiples of reflector at base of Cretaceous. The geologic setting of borehole 6001 may be represented by location B on the pro file (near shot point 400) with respect to its position relative to the inferred Triassic-Jurassic basin. The basalt found in borehole 6001 may be represented by the strong reflector at a reflection time of about 0.7 seconds (between shot points 110 and 230 below location A), because this reflector occurs in the area of seismic line No. 5 at a depth below sea level similar to the depth of the basalt in the borehole. lies close to the northern end of a northeast- squeezed from the cores recovered from the trending basement ridge that is bordered on borehole. E. G. A. Weed described and sampled the northwest by a parallel broad basin that cores during virtually the entire period of the underlies Nantucket Sound and extends south- drilling operations, managed the logs of the westward under the Continental Shelf (Klit- data obtained, and aided in training and super gord and Behrendt, 1977). vising the technicians who assisted from time to time in processing cores. E.G. Rhodehamel par ACKNOWLEDGMENTS ticipated in on-site operations during the drill F. A. Kohout l and M. H. Bothner set up the ing of the saprolite and basalt in the lower part equipment and conducted on-site determinations of the borehole and during the final logging of of tests of salinity and pH of interstitial water the well. He also interpreted the logs and pro vided tentative correlations of these with other 1 All persons mentioned in these acknowledgments are from the USGS unless an affiliation is otherwise indicated. wells of the Atlantic Coastal Plain. J. A. Commeau made partial chemical anal ducted the drilling and coring operations des yses of the core materials by X-ray fluorescence. pite severe winter conditions. Janet R. Moller L. J. Poppe prepared X-ray diffraction patterns of Falmouth, Mass., drafted most of the illus and made qualitative mineralogic analyses of trations for this paper. the cores. S. A. Wood assisted in part of the on-site METHODS work with the cores and also assembled and The U.S. Army Corps of Engineers began proofed some tabular material and parts of the drilling on November 9, 1975, with a Failing 2 text and assembled information from some of 2000 rotary rig. Our objective was to core the the references. entire hole to provide as much stratigraphic E. H. Walker participated in the early on- information as possible. Several methods, in site salinity determinations and provided advice cluding split-spoon coring, punch or 'driven bar on local ground-water conditions on Nantucket. rel coring, as well as rotary coring, were used W. S. Barrett of Nantucket, Mass., gave im to improve recovery in the upper unconsolidated portant assistance in arrangements with local glacial sands and gravels. Nevertheless, recov groups and contractors on Nantucket, lent ad ery was poor (10.3 percent) throughout the vice and counsel on local conditions, and pro upper 120 m of section until casing (24.5 cm or vided history, samples, and original paleontol- 9% in. I.D.) was set at 125 m. From that point ogic analyses from the well drilled in 1933 at on, best recovery (45.5 percent) was obtained Coskata. in clay-rich sediments using a core barrel 15.2 The following assisted in the work of de cm (6 in.) I.D. by 6.1 m (20 ft) long, designed scribing, sampling, photographing, and packing by the Corps of Engineers. Where hard rock cores at various times during the coring of the was penetrated, a conventional petroleum core well: Susan Wieber, Rebecca Belastock, Charles barrel with a diamond rock-coring bit (Hycalog O'Hara, Ellen Davie, Raymond Hall, Robert 9.1 m (30 ft) long; 6.35 cm (2V2 in.) I.D.) was Commeau, John Schlee, James Robb, W. M. used and obtained 73 percent recovery. Ferrebee, Lyle McGinnis, Anna Sundberg, Immediately after recovery, cores were de Christina Schoen, John Dunlavey, David De- scribed, photographed, and sampled for tex- laney, Patricia Forrestel, Stanley Locker, and tural, hydrocarbon, mineralogic, paleontologic, Paul Cousins. and water analyses. Squeezing for pore water John Baker and Michael Frimpter supervised analysis was carried out immediately by a hy the original arrangements for the water re draulic press (Manheim, 1966) and salinity sources test well and lent advice and counsel values obtained using an Endeco type 102 re- during later stages of the program. David De- fractometer. Some microscopic examination of laney aided extensively in the interstitial water the samples was carried out on the well site. chemistry studies during the drilling oper ations. In the laboratory, samples were examined for James Lentowski, executive secretary of the microfossils, including Foraminifera, nanno- Nantucket Conservation Foundation, arranged fossils, pollen, and spores. At places where lith- for the clearing of the site prior to the drilling ologic changes were seen or at one depth in each and for the restoration of the site after comple core, mineral content was assessed by L. J. tion of the project. Poppe, using a Norelco X-ray diffractometer The late Austin Tyrer, local water-well drill equipped with a graphite curved-crystal mon- ing contractor, drilled freshwater supply wells ochromator and a proportional counter alined for the program and rendered assistance in to record copper K« radiation (A= 1.5418 A). numerous logistic problems that arose during Textural analyses were carried out with a the operations. Rapid Sediment Analyzer (Schlee, 1966) and a Larry J. Nutter ran electric logs (self-poten Coulter Counter Model TAII by Sally Wood, tial and resistivity) of the upper 125 m of the Peter Johnson, and Wayne M. Ferrebee. Hydro well. carbons were assessed by Robert Miller, David
H. Peyton Herman supervised the crew of the - Trade names in this publication are used for descriptive pur poses only, and do not constitute endorsement by the U.S. Geo U.S. Army Corps of Engineers, who ably con logical Survey. Schultz, and George Claypool of the USGS by LITHOLOGIC soxhlet extractions and gas chromatography. COLUMN GROUND LEVEL 0 FT 0 METERS Two potassium-argon ages were determined by GAMMA RAY API SEA LEVEL R.F. Marvin, H. H. Mehnert, Kinyoto Futa, and 35.9 FT (I0.9M Violet Merritt. Potassium content was deter mined using an Instrument Laboratories Flame Photometer with a lithium internal standard. Permeability and porosity measurements were -GAMMA RAY carried out by Core Lab., Inc. Chemical com positions were obtained by Judith A. Commeau, using a Diano XRF 8000 automated X-ray fluorescence analyzer. Sample preparation was by the methods of Rose, Adler, and Flanagan -BASE OF CASING (1963). Carbon-14 date W-3542 was measured SP in the laboratory of the USGS by Meyer Rubin.
RESULTS STRATIGRAPHY GENERAL LITHOLOGY To a depth 3 of 457 m, the borehole pene trated unconsolidated and semiconsolidated sedimentary clastic detritus that ranges in tex ture from clay «0.004 mm) to cobbles (128 mm). Below 457 m, a saprolite, composed mostly of clay, grades abruptly at about 470 m into partially weathered or altered basalt that extends to the bottom of the hole at 514 m. The sedimentary section can be divided into three lithologic zones. The upper zone, from the surface to 128 m, is dominated by coarse sand and gravel and a few thin beds of clay and silt; the middle zone, from 128 to 349 m, is composed mostly of silty clay showing increasing consoli dation as the depth increases, interbedded with a few clayey, silty, sandy beds (3-12 m thick) and indurated siltstone beds as much as 30 cm thick. The lower zone, from 349 to 457 m, con tains soft, unconsolidated, water-saturated, clayey sand interrupted by clay layers 3 to 6 m thick. The lithology of the section from the bore hole is shown in columnar section in figure 3. UPPER ZONE Lithology. In the upper zone (0-128 m), OHMS M /M sands range in texture from medium to very TD 1686 FT RESISTIVITY 0. .100 coarse grained and range in color from light 514 M tans, grays, and olives to bright green. Pea-size (<1 cm) gravel is most common but coarse FIGURE 3. Columnar section of borehole 6001 gravel and cobbles apparently are scattered showing lithology, core recovery (solid black, left side of column; small arrows indicate driven 1 All depths are from ground level (10.9 m above sea level). cores), self potential (SP), caliper, induction re sistivity, and gamma ray logs. See figure 7 for explanation of lithologic symbols. throughout the section, especially between 60 minor amounts of illite and smectite; chlorite and 80 m. Two thin zones cored at 35 and 63 m is absent. Minor amounts of mixed layer smec- contain a mixture of gravel, sand, silt, and tite-illite are found toward the base of the zone. clay, and may be glacial tills or weathered soil Quartz, rare amounts of plagioclase feldspar, zones. Shell fragments, as much as 7 cm across, goethite, gibbsite, hematite, siderite, and occa form layers that are most common between 38 sionally anatase constitute the main non-clay and 61 m. Greensand having a matrix of silt fraction. The mineralogy of this interval is thus and clay-size glauconite was first found at 91 m characteristic of a heavily weathered and and, though recovery was poor, appears to leached soil, probably formed under tropical, dominate at least to 107 m and perhaps as deep humid conditions. as 126m. Coal. A bed of lignite/subbituminous coal Mineralogy. Dominant clay minerals in the at least 20 cm thick was found at 328 m. When upper 120 m of the section are illite and minor the core was first recovered, freshly exposed kaolinite; chlorite and dioctahedral vermiculite surfaces were dark brown but turned black are also common in several intervals. Smectite, within seconds after exposure to the air. Anal which was observed in several samples from yses by George E. Claypool, USGS, showed that this zone, is probably contamination from the it is a relatively pure coal containing 58.8 per drilling mud because it shows extremely sharp cent organic carbon. Soxhlet extraction yielded and well ordered X-ray diffraction peaks, quite 2.68 percent bitumen. Of this, 0.14 percent is unlike the mixed-layered assemblages usually composed of saturated hydrocarbon, 0.18 per found in such detrital sediments. The coarse cent is nominal aromatic hydrocarbon material, fraction comprises mainly quartz and plagio- and the balance of 2.36 percent is nonhydro- clase feldspar. Calcite and aragonite are present carbon extractable organic matter. Its total hy in strata containing shells. drocarbon concentration of 3,181 ppm and a hydrocarbon-to-organic carbon ratio of 0.54 are MIDDLE ZONE typical of low-rank coals. The saturated-to- Lithology. The middle zone (128-349 m) aromatic hydrocarbon ratio of 0.76 is much contains mostly variegated clay and fewer higher than typical humic coals, suggesting a interbeds of light-gray sand. The dense, com higher content of waxy tissues in this coal. pact, and silty clay ranges in color from white Thermal analysis/pyrolysis showed only 12.2 to red, yellow, brown, purple, olive gray, and percent of the organic carbon recoverable as black; in many places, it is mottled in combi pyrolytic volatiles. This relatively small amount nations of these colors. The black and dark- indicates that the organic matter of the coal gray layers contain abundant lignite and many would be a relatively inefficient generator of leaf imprints; at least one interval contains petroleum hydrocarbons. lignite/subbituminous coal at 328 m (described Gas chromatography of the products of py- below). Particles of lignite are also scattered rolysis showed that, although the coal is capable throughout most of this middle zone. Inter- of generating light (C10-C2n ) paraffin hydro bedded sands are commonly gray to brown, carbons, it is thermally immature and has not highly micaceous, kaolinitic, and contain done so. The temperature of maximum pyrolysis abundant lignite. Very fine to medium-grained yield (450°C) indicates a low-temperature his sand is most abundant, but coarse to very tory, or lignite/subbituminous rank (G. E. coarse material is present. Sand is more com Claypool, written commun., 1975). These re mon than clay from about 128 to 213 m, where sults indicate that sediments in this part of the as clay tends to be more common below 213 m. shoreward edge of the Atlantic continental mar The sediments are more indurated toward the gin sediment wedge have never been buried base of the zone at 349 m; some layers are hard deeply enough to generate mature petroleum cemented siltstone. hydrocarbons. Thus, unless migration has taken Mineralogy. Clay minerals are the most place, any accumulations of petroleum hydro common constituents of this zone. Of these, carbons probably occur far seaward of the Nan- kaolinite is most abundant accompanied by tucket site in areas where source sediments have been buried much more deeply than those these probably represent minimum ages, and at Nantucket. the basalt may well be at least Triassic in age.
LOWER ZONE The types of clay and other alteration min erals in the basalt are not the result of weather Lithology. In the lower zone (349-457 m), ing processes as is the kaolinite of the saprolite sandy sediments are predominant; they are un- zone. Alteration within the basalt itself prob consolidated and mostly light gray or occasion ably took place as a result of hydrothermal ally tan, and contain rare pebbles (<1 cm) and processes early in the history of the rock, and layers of yellowish clay. The sand is fine to very thus the ages obtained may not be as much in coarse grained and has an abundant matrix of error as the existence of alteration might other clay that is mostly kaolinite. The cores recov wise suggest. The saprolite, however, is prob ered were usually soft and watery. Interbedded ably the result of later subaerial weathering. clay horizons, a few meters to 10 m thick, are Chemistry. Chemical analyses (table 1) for light gray, red, and yellow, commonly mottled, very sandy, silty, and micaceous. Si02, Al20:i, Fe203, MnO,, MgO, CaO, Na20, K20, TiOL>, and P205 and modal mineralogical Mineralogy. The abundant sand in the analyses by X-ray diffraction were made for lower zone contains mostly quartz and minor samples taken from the cores at 1- to 3-m inter plagioclase feldspar. Clay minerals are mainly vals. Fluctuations in abundances (fig. 4) of kaolinite, lesser amounts of illite, and rare some elements (expressed as oxides) appear to smectite. Neither chlorite nor vermiculite was reflect mainly the extent of weathering and observed. leaching. For example, the saprolite zone from In summary, the upper 128 m zone of sedi about 470 m to 457 m shows upward decreasing ments is almost entirely sand and gravel, the concentrations of MgO, Si02, P20D, CaO, and middle 221-m zone is mostly clay and silt, and Na20 and increasing concentrations of A1203, the lower 108 m zone is mostly sand. Fe20:;, and Ti02. The first five elements thus have been removed, apparently as deep weath SAPROLITE AND BASALT ering has proceeded with time, and the last Lithology. At 457 m, the stratified sands three have concurrently increased as part of and clays are in contact with an unbedded ma residual, refractory mineral constituents. The roon clay containing many rounded blebs and K20 and Mn02 contents show only slight de veins of white clay. The white structures closely creasing trends in this interval. resemble those in the veined amygdaloidal ba Below 470 m, variations are more complex. salt that underlies the clay zone. We concluded that the maroon and white clay is a saprolite Several samples in which MgO content and the derived by weathering-in-place of igneous rock ratio of Si02/Al20:: are large correlate with the having similar structure. At about 470 m, the occurrence of the mineral saponite. Saponite clay grades into hard partially weathered or (not to be confused with the term "saprolite" altered basalt that is maroon to brown and above) is a magnesium-rich smectite (mont- aphanitic to finely crystalline; the basalt is morillonite group minerals) having relatively veined with calcite and has vesicles filled with low aluminum content. Its idealized structural zeolite or saponite. Toward the bottom of the formula (Ross and Hendricks, 1945) is: hole at 514 m, the basalt is bluish gray and con Na0.:-i, tains many amygdules and veins consisting of r red, white, and green zeolites, saponite, and cal Mg3 {Si3.B7 A10.,3> 010{OH2) cite. The chemical composition for sample 6001- Two samples of the basalt were dated by the 120-5 (55-58 cm) gives the following calcu K-Ar methods. A sample from 485.7 m gave an age of 183±8 m.y. (Early Jurassic); the other lated structural formula: sample taken at 513.8 m, was dated at 164±3 {Na0.n;i Kn.oi Ca0.i0} m.y. (Middle Jurassic). Because the basalt in t T both samples was partially altered, however, {Mg2.49 Fe0.20 A10. 10> {Si.,.^ A10.«3> 010 {OH2}
8 TABLE 1. Partial chemical and X-ray modal analyses of volcanic rock and saprolite [Chemical analyses by J. A. Commeau; X-ray diffraction analyses by L. J. Poppe and J. C. Hathaway] Sample No.1 ______. 6001-116-1 6001-116-2 6001-116-2 6001-116-2 6001-116-3 6001-116-4 (15cm) (10cm) (60cm) (90cm) (107cm) (25-50 cm) Depth (m) 456.5 457.5 458.0 458.3 459.6 460.0 Material _. Gray Maroon Maroon Maroon Dark red Yellow sedi clay with clay with clay with clay, blebs. mentary white white white clay. blebs. blebs. blebs. Partial chemical analyses for major oxides in weight percent from X-ray fluorescence Si02 ______38.51 26.80 19.37 33.01 A1203 ______27.45 18.41 28.53 21.27 Fe203 ______2.21 27.30 24.89 13.34 Mn02 ______.03 .11 .12 .05 MgO ______.96 .83 .78 .46 CaO ______.11 .13 .12 .14 Na20 ______.37 .50 .58 K2O ______.00 .00 .005 .02 Ti02 ______3.18 2.91 3.06 .85 P2On ______.00 .04 .05 .06 Partial total ______72.82 77.03 77.505 69.20
______Estimated modes from X-ray diffraction Kaolinite ______99 75 72 75 75 87 Smectite (montmorillonite group other than saponite) ___ Saponite ______Mixed layered smectite-chlorite _ Chlorite ______Illite _-______Talc ______Heulandite ______Stilbite ______Analcime ______Prehnite ______Potassium feldspar ______Plagioclass feldspar ______Calcite ______Tr. Hematite ______25 28 25 25 13 Other ______Quartz tr. Quartz tr. Sample No.1 ______6001-116-4 6001-116-5 6001-116-6 6001-117-1 6001-117-2 6001-117-3 (90cm) (40cm) (20cm) (50cm) (55cm) (55cm) Depth (m) ______460.5 461.2 462.0 462.7 464.0 465.2 Material ______Maroon Maroon Maroon Maroon Dark- 'Maroon ** clay with clay with clay with clay with maroon clay white white white white clay with with white blebs. blebs. blebs. blebs. green amygdukg amygdules Partial chemical analyses for major oxides in weight percent from X-ray fluorescence SiO, ______31.37 34.54 43.64 Al.0.1 ______23.31 20.09 14.87 Fe.O, ______20.36 23.04 15.76 MnO, ______.11 .11 .05 MgO ______.00 .33 1.98 CaO ______.17 .53 1.13 Na,0 ______.49 .98 1.68 K,O ______.16 .77 .89 TiO2 ______2.96 3.14 2.67 P2O5 ______.19 .21 .35 Partial total ______79.12 83.74 83.02
Estimated modes from X-ray diffraction Kaolinite ______70 90 79 75 30 15 Smectite (Montmorillonite 55 69 group other than saponite) ___ Saponite ______Mixed layered smectite-chlorite _ TABLE 1. Partial chemical and X-ray modal analyses of volcanic rock and saprolite Continued Estimated modes from X-ray diffraction Chlorite ______Illite ______Talc ______Heulandite ______Stilbite ______Analcime ______Prehnite ______Potassium feldspar ______Tr. Plagioclase feldspar ______Tr. Calcite ______Hematite ______20 10 21 25 10 16 Other ______Quartz tr. Quartz tr. Sample No.1 ______6001-117-4 6001-118-1 6001-118-3 6001-118-3 6001-118-3 6001-119-1 (25 cm) (3-5 cm) (47-49 (109-110 (110-111 (l-2cm) cm) cm) cm) Depth (m) 465.4 465.5 467.8 468.4 468.5 469.4 Material _. Maroon Red clay Amygdules Red clay Veins and Red basalt clay with amygdules. white amygdules Partial chemical analyses for major oxides in weight percent from X-ray fluorescence _____ SiO. ______42.30 46.73 47.53 54.29 40.96 Al-6:, _--______----- 17.79 14.74 15.77 16.83 15.70 Fe,O, ______15.88 8.75 16.77 5.83 14.42 MnO. ______.05 .05 .05 .04 .06 MgO ______2.04 2.05 1.10 3.77 .16 CaO ______1.24 .82 1.40 .78 4.82 Na.O ___ _ ; ______-_ 1.48 3.32 2.04 3.64 K.O ______.16 .34 1.18 .42 .95 TiO, ______1.96 .82 2.45 .69 2.09 P»O, ______.40 .08 .31 .06 .27 Partial total ______83.30 74.38 89.88 84.75 83.07 Estimated modes from X-ray diffraction Kaolinite ______15 20 Smectite (montmorillonite group other than saponite) __ 69 65 90 53 90 20 Saponite ______Mixed layered smectite-chlorite _ Chlorite ______Illite ______Talc ______Heulandite ______Stilbite ______Analcime ______Prehnite ______Potassium feldspar ______Tr. Plagioclase feldspar ______30 Tr. 70 Calcite ______Tr.? Hematite ______15 15 8 17 6 15 Other ______Quartz 1 Unidentified Unidentified mineral. mineral. Sample No.1 ______6001-120-1 6001-120-1 6001-120-4 6001-120-4 6001-120-5 6001-120-5 (4-6 cm) 2 (95-96 (48-49 (66-69 (44-46 (55-58 cm) 2 cm) cm) cm) cm) Depth (m) ______472.7 473.6 476.5 476.7 477.6 477.8 Material ______Maroon Basalt White White Red vein Yellow basalt with green calcite vein calcite vein vein amygdules Partial chemical analyses for major oxides in weight percent from X-ray fluorescence SiO2 ______-__ 39.94 38.93 1.54 18.84 37.62 45.55 AlsOa ______12.40 12.37 .37 4.74 8.65 8.45 Fe203 ______11.51 11.78 .46 1.05 6.01 3.61 Mn02 ______.17 .16 .70 .59 .33 .00 MgO ______5.14 4.51 4.71 4.48 12.61 22.61 CaO ______7.63 6.23 46.89 33.93 7.62 1.29
10 TABLE 1. Partial chemical and X-ray modal analyses of volcanic rock and saprolite Continued
Partial chemical analyses for major oxides in weight percent from X-ray fluorescence Na2O ______4.68 2.80 3.08 2.65 2.51 3.26 K2O ______.54 1.04 .00 .56 .49 .11 TiO2 ______1.55 1.51 .00 .00 .01 .00 P^Os ______.19 .18 .13 .07 .00 .00 Partial total ______83.75 79.51 57.88 66.91 75.85 84.88
Estimated modes from X-ray diffraction Kaolinite ______-___ Smectite )montmorillonite group other than saponite) ___ -20 - 68 "10 "62 =100 Saponite ______Mixed layered smectite-chlorite _ Chlorite ______Illite ______Talc ______Heulandite ______Tr. 20 20 Stilbite ______Analcime ______Prehnite -______Potassium feldspar ______Tr. Plagioclase feldspar ______60 4 2 Calcite ______8 15 99 53 11 Hematite ______12 12 6 Other ______Sample No.T ______6001-120-5 6001-120-5 6001-121-1 "'6001-121- "6001-121- 6001-121-7 (64-66 (73-75 (22cm) 1(30-31 1(30-31 (27-29 cm) cm) cm) cm) cm) Depth (m) ______477.9 478.0 479.4 479.5 479.5 485.3 Material ______Maroon White White Greenish Maroon Green basalt crumbly vein amygdules basalt vein vein Partial chemical analyses for major oxides in weight percent from X-ray fluorescence SiO. ______41.34 46.27 6.59 50.44 43.12 38.80 AU), ______12.85 10.32 1.53 15.58 13.99 7.34 Pe2O3 ___-______13.28 1.51 1.41 4.63 14.21 10.09 MnO2 ______.15 .23 .95 .07 .13 .08 MgO ______10.80 12.39 5.32 7.01 6.95 19.45 CaO ______5.72 5.14 42.57 .91 1.59 1.89 Na.O ______3.12 2.32 2.65 2.18 3.30 K2O ______1.04 .23 .22 .40 .63 .08 TiO3 ______1.77 .01 .06 .18 2.07 .65 P.O.-, ______.24 .00 .12 .00 .25 .05 Partial total ______90.31 78.42 61.42 81.40 86.24 78.43
Estimated modes from X-ray diffraction Kaolinite ______Smectite (montmorillonite group other than saponite) _ 3 30 80 80 33 10 Saponite ______15 22 80 Mixed layered smectite-chlorite _ Chlorite ______Illite ______Talc ______10 Heulandite ______10 Stilbite ______10 Analcime ______Prehnite ______Potassium feldspar ______Plagioclase feldspar ____ 42 28 Tr. Calcite ______10 10 4 90 2 2 Hematite ______13 3 15 Other ______
11 TABLE 1. Partial chemical and X-ray modal analyses of volcanic rock and saprolite Continued
Sample No.1 ______6001-121-7 6001-121-7 6001-122-1 6001-122-2 6001-123-1 6001-123-2 (64-70 cm) (67-70 cm) (35-37 cm) (90-95 cm) (24-26 cm) (13-15 cm) Depth (m) ______485.7 485.7 487.1 488.9 489.4 491.3 Material ______Maroon Maroon Maroon Green Gray Gray basalt basalt basalt amygdules basalt with basalt green amygdules Partial chemical analyses for major oxides in weight percent from X-ray fluorescence Si02 ______41.19 40.58 38.06 38.61 41.91 AlaOa ______14.08 11.77 6.98 10.38 11.96 Fe->O3 ______13.18 14.38 10.91 10.73 11.56 MnO2 ______.11 .12 .06 .10 .16 MgO ______6.87 11.41 23.66 9.40 7.59 CaO ______8.92 6.68 .96 6.50 3.31 Na2O ______3.45 2.66 2.87 2.79 4.14 K2O ______.62 .51 .01 .37 1.14 TiO2 ______1.68 1.70 .20 1.41 1.84 P«O- ______23 22 01 16 24 'llllllllllllll" 9o'.33 9o!o3 SB.12 SQA5 83.'85
Estimated modes from X-ray diffraction Kaolinite ______Smectite (montmorillonite group other than saponite) ___ 10 20 Saponite ______20 10 20 89 30 Mixed layered smectite-chlorite _ Chlorite ______Illite ______Talc ______Heulandite ______Stilbite ______Analcime ______Prehnite ______Potassium feldspar ______Plagioclase feldspar _ ____ 67 67 65 59 68 Calcite ______Hematite ______13 13 15 11 11 12 Other ______Sample No.1 ______6001-123-4 6001-124-1 6001-124-3 6001-124-3 6001-124-3 6001-124-4 (13-15 cm) (73cm) (55-58 cm) (74-76 cm) (112-114 (50cm) cm) Depth (m) ______495.4 498.8 503.0 503.2 503.5 505.4 Material ______Maroon Maroon Red basalt Orange Red basalt Red basalt with basalt vein "rotten" amygdules rock Partial chemical analyses for major oxides in weight percent from X-ray fluorescence SiO. ______44.46 46.08 46.21 55.66 38.89 39.34 ALO, ______13.67 13.82 14.99 19.09 14.99 15.17 Fe,O3 ______12.92 11.77 10.50 9.40 13.85 10.98 MnO2 ______.14 .18 .11 .54 .15 .20 MgO ______4.45 8.34 4.35 3.61 5.88 16.32 CaO ______4.37 5.04 1.74 2.73 1.85 5.73 Na2O ______5.86 4.86 5.68 4.33 1.49 1.73 K2O ______1.91 1.17 1.20 1.73 3.12 .55 TiO2 ______2.50 1.70 1.29 1.42 1.40 .64 P2O5 ______.33 .22 .11 .23 .10 .13 Partial total ______90.61 93.18 86.18 98.74 81.72 90.79
Estimated modes from X-ray diffraction Kaolinite ______Smectite (montmorillonite group other than saponite) ___ 20 18 16 Saponite ______22 Mixed layered smectite-chlorite _ 30 30 Chlorite ______Illite ______Tr. 57 Talc ______
12 TABLE 1. Partial chemical and X-ray modal analyses of volcanic rock and saprolite Continued
Estimated modes from X-ray diffraction Continued Heulandite ______Stilbite ______Analcime ______32 Prehnite ______Potassium feldspar ______10 5 Plagioclase feldspar ______35 70 66 70 39 54 Calcite ______Hematite ______13 12 11 9 14 11 Other ______
Sample No.1 ______6001-124-4 6001-125-1 6001-126-1 6001-126-2 6001-126-2 6001-126-5 (80cm) (0-1 cm) (1-2 cm) (18-20 cm) (20-22 cm) (23-24 cm) Depth (m) ______505.7 507.2 508.4 509.6 509.6 512.9 Material ______Maroon Maroon Maroon Gray Maroon Maroon basalt basalt basalt basalt basalt with basalt white crystals Partial chemical analyses of major oxides in weight percent from X-ray fluorescence Continued SiO, ______43.50 43.74 46.91 49.12 38.67 41.60 A12O:! ______12.68 11.73 13.62 16.50 19.42 12.92 Fe2O3 ______11.84 11.63 12.10 12.83 7.42 11.78 MnO2 ______.16 .15 .15 .13 .07 .15 MgO ______.._ 6.43 6.33 6.64 6.60 4.48 7.00 CaO ______5.05 5.13 5.87 9.67 20.35 6.37 Na,O ______5.57 5.80 4.85 1.13 5.63 K2O ______.88 .75 .87 .37 .36 .90 TiO2 ______1.76 1.78 2.15 1.71 .82 1.74 P2O, ______.21 .20 .21 .24 .15 .22 Partial total ______88.08 87.24 88.52 102.02 93.47 88.31
Estimated modes from X-ray diffraction Continued Kaolinite ______Smectite (montmorillonite group other than saponite) ___ Saponite ______Mixed layered smectite-chlorite _ 15 15 15 10 Chlorite ______10 5 Illite ______tr Talc ______Heulandite ______Stilbite ______Analcime ______20 tr 55 Prehnite ______15 80 Potassium feldspar ______tr tr 20 Plagioclase feldspar ______73 53 72 62 20 Calcite ______tr Hematite ______12 12 12 13 8 Other ______
Sample No.1 ______6001-126-5 6001-126-5 6001-126-5 (85-88 cm) (105-107 (110-114 cm) cm) Depth (m) ______513.6 513.8 513.9 Material ______Red basalt Basalt Gray basalt with white crystals Partial chemical analyses for major oxides in weight percent from X-ray fluorescence SiO, ______28.20 48.56 AW), ______11.65 16.34 Fe203 ______8.87 12.63 MnO2 ______.19 .15 MgO ______6.87 6.84 CaO ______21.31 9.33 Na2O ______1.63 4.20 K2O ______.08 .89 Ti02 ______.36 1.97 P,O5 ______.10 .27 Partial total ______79.26 101.18
13 TABLE 1. Partial chemical and X-ray modal analyses of volcanic rock and saprolite Continued
Estimated modes from X-ray diffraction Kaolinite ____-______Smectite (montmorillonite group other than saponite) _ 10 Saponite _____ 20 Mixed layered smectite-chlorite _ 20 Chlorite ______Illite ______Tr. Talc ______Heulandite ______Stilbite ______Analcime ______Prehnite ______10 Potassium feldspar ______8 Plagioclase feldspar _____ 15 69 77 Calcite ______- 35 Hematite ______9 11 13 Other ______.__
u As 2 above, but no collapse, even at 750° C. * Magnesium calcite (about 18 percent MgCO::). 5 Amygdules. "Host basalt.
MgO S,02/AI 203 P205 Ti02 Fe203 CaO Mn02 Na20 K20 Percent Percent Percent Percent Percent Percent Percent 23456 0001 03 0501234 10 20 30 0 10 30 50 00 05 10 O I 2 3 4 5 6 0 I ' ' ' ' ' I ' ' ' '
c = Analcime Ch = Chlorite Ct=Calcite Hd = Heulandite K = Kaolinite Pr = Prehnite Sm = Smectite Sp = Saponite Tc=Talc
FIGURE 4. Diagram showing variation of chemical elements and minerals as depth increases in the basalt and saprolite zones of borehole 6001. See figure 5 for explanation of symbols, which depict type of sample or rock. These values are within the range of saponite Manganese content (fig. 6) generally shows composition shown by Ross and Hendricks increases where CaO content is large. (1945), and Grim (1968). Many of the samples were selected to assess As shown in figures 4 and 5, Ti02 and P20r, the composition of vein and amygdaloidal min tend to fluctuate together, except in the upper erals. Immediately below the saprolite, most saprolitic zone, where Ti02 increases upward veins are either calcite or saponite, whereas and P205 decreases. many amygdules are filled by zeolites. As the
14 3.0-
°-2 Percent 0.5
FIGURE 5. Diagram showing variation of TiO,. and P.O.-, in the basalt and saprolite zones of borehole 6001.
depth increases, heulandite and stilbite are suc ceeded by analcime and prehnite.
PALEONTOLOGY
COSKATA WELL PLEISTOCENE In the upper 44 m of sand and gravel, benthic O and pelagic foraminifers of Pleistocene age are CL 0.4 identical to those recovered in borehole 6001 and are indicative of deposition in a nearshore shelf environment similar to that present today in the New England region.
PLIOCENE OR MIOCFNE In silty clay from 46 to 55 m, a Pliocene or *.- Percent 30 40 Miocene assemblage contains a sparse foramini- CdO feral fauna. A few planktic specimens appear to be Neogloboquadrina pseudopacJiyderm.a 6.a DiagramTV showingi_ variation of MnO, and CaO in the basalt and saprolite zones of borehole 6001. (Cita, Primoli Silva, and Rossi). Benthic forms
15 include Cibicidoides ftoridanus (Cushman), foraminifers, ostracodes, dinoflagellates, and, Bulimina marginata (d'Orbigny), Oridorsalis especially, spores and pollen (sporomorphs). umbonatus (Reuss), and Florilus grateloupi Pleistocene samples contain only ostracodes and (d'Orbigny), probably all deposited in a mid- foraminifers; Eocene samples yield dinoflagel shelf environment. lates and sporomorphs; and Upper Cretaceous beds contain sporomorphs, rare agglutinated EOCENE benthic foraminifers, and a few casts of mol- In silty clay from 55 to 75 m, early Eocene lusks. foraminiferal faunas contain numerous benthic PLEISTOCENE forms and small planktic specimens, most of which belong- to indeterminate species. Those The Pleistocene microfossil assemblages are species that are recognizable and diagnostic are limited to the medium to coarse quartz sands in Acarinina broedermanni (Cushman and Ber- the interval from 38 m to 45 m. The total Pleis mudez), Morozovella cf. M. trichotrocha (Loeb- tocene section is inferred to extend to 85 m lich and Tappan), Guembelitria cf. G. colum- depth. Twenty-one species of benthic foramin biana (Howe), Bulimina pseudocacumenata ifers are represented, but specimens are rare. Olsson, Turrilina robertsi (Howe and Roberts), The predominant forms are Elphidium orbic- Pseudohastigerina micro, (Cole), Alabamina ulare (H. B. Brady), Elphidium clavatum wilcoxensis Toulmin, Gyroidinoides octocamer- (Cushman), Cibicidoides lobatulus (Walker atus (Cushman and Hanna). This assemblage and Jacob), Glabratella wrightii (H. B. was probably deposited in outer continental Brady), Buccella inusitata Andersen, and Buc- shelf conditions. cella frigida (Cushman). Modern representa tives of these species inhabit the shallow waters PALEOCENE adjacent to Nantucket Island, and the Pleis In silty clay of Paleocene age from 75 to tocene sediments containing them presumably 102 m, foraminiferal assemblages contain many were deposited under similar conditions. species common to the Aquia Formation of A small but well-presrved ostracode assem Maryland and the Vincentown Formation of blage was recovered from a depth of 45 m. The New Jersey. The planktic and benthic species are sample contains abundant molluscan fragments, diverse and include Acarinina tribulosa (Loeb- and 19 species of ostracodes: lich and Tappan), A. aquiensis (Loeblich and Baffinicythere emarginata (Sars) ; Benson- Tappan), A. pentacamerata (Subbotina), A, ocythere americana Hazel; B. sp. A of Valen strabocella (Loeblich and Tappan), A. esnaen- tine (1971) ; B. sp. B of Valentine (1971) ; B. sis (Leroy), Morozovella aequa (Cushman and sp. D of Valentine (1971) ; B. sp.; Cytheridea Renz), Subbotina triloculinoides (Plummer), sp. A of Valentine (1971); Cytherura sp.; Pseudohastigerina micra (Cole), Alabamina Finmarchinella angulata (Sars) ; F. finmar- midwayensisC!) Brotzen, Trifarina wilcoxensis chica (Sars) ; Hemicy'there villosa (Sars) ; (Cushman and Ponton), Gyroidinoides octo- Hemicytherura clathrata (Sars) ; Leptocythere cameratus (Cushman and Hanna), Turrilina angusta Blake; Loxoconcha aff. L. granulata robertsi (Howe and Roberts), and Anomali- Sars of Valentine (1971) ; Microcytherura noides midwayensis (Plummer). This assem choctawhatcheenis (Puri) ; Muellerina canaden- blage contains more planktic specimens and sis (Brady) ; M. aff. M. lienenklausi (Ulrich more deep water benthic specimens than and Bassler) of Hazel (1970) and of Valentine younger sediments in the hole, but probably still (1971) ; Sclerochilus sp. C of Valentine (1971) ; reflects outer shelf conditions during deposi and Xestoleberis sp. tion. All the ostracode species range throughout the Holocene and Pleistocene, and a few also BOREHOLE 6001 range into the Pliocene. The modern geographic Fossils are scarce in the core, but Pleistocene, distribution of 15 of these species is known Eocene, and Upper Cretaceous assemblages (Hazel, 1970,1971; Valentine, 1971). have been identified; they include benthic Hazel (1970) established the presence of an
16 ostracode faunal province boundary at Cape Wetzeliella symmetrica Weiler, W. articulata Cod that delineates the cold temperate Nova Eisenack, W. sp., Pentadinium sp., Cordospha- Scotian faunal province to the north from the eridium fibrospinosum Darcy and Williams, and mild temperate Virginian province to the south. Membranosphaera maestrichtica, Samoilovitch. The boundary is found somewhat to the north All these forms have been recorded from lower of Nantucket Island. The fossil ostracode as Tertiary sedimentary rocks and the assemblage semblage from the Nantucket well is composed is considered to be of Eocene age (Fred May, (with two exceptions) of two groups of species: written commun., 1976). those that now range from the Arctic or sub- The palynomorphs of the greensand include Arctic to the Nova Scotian-Virginian province a single specimen of the Paleocene to basal boundary or into the Virginian province; and middle Eocene genus Thomsonipollis, among an species that are restricted to the Virginian and assemblage of reworked Cenomanian species Nova Scotian provinces. Typical southern forms and modern contaminants. Cenomanian forms are absent. include Peromonolites allenensis Brenner, Tri- The fossil ostracode assemblage, though less colporopollenites triangulus Groot, Penny and diverse, resembles the modern Cape Cod as Groot, Ajatipollis cf. A. tetraedralis (Bolkhovi- semblage, and therefore confirms the inference tina) Krutzsch, Cyathidites minor Couper, from the foraminifers that the marine climate Cicatricosisporites hallei Delcourt and Spru- at the time of deposition approximated the mont, and Retitricolpites minutus Pierce. Mod present mild to cold temperature climate off ern forms are Quercus sp., Pinus sp., Alnus sp., shore from Nantucket Island. Deposition took Corya sp., Myrica sp., and members of the place during a period of raised sea level in the familes Chenopodiaceae and Ericaceae. Pleistocene, possibly during the Sangamon Interglaciation, or perhaps marking an interval UPPER CRETACEOUS of glacial retreat during the Wisconsin Glaci- Upper Cretaceous beds were identified by ation. A radiocarbon date based on marine fos their spore and pollen assemblages, which can sils of > 40,000 years B.P. at 57.3 m does not be correlated with those of the New Jersey confirm this interpretation but at least does not Coastal Plain formations. invalidate it. Abundant palynomorphs of latest Campanian Pleistocene deposits also are found in the sea Age are the youngest Cretaceous forms identi cliffs at Sankaty Head on Nantucket (Cushman, fied. They were found in the black clay that 1904; Wilson, 1905). In a recent study, Gustav- marks the top of the middle lithologic zone at son (1976) reevaluated the age and paleoenvir- 128.8 m and are equivalent to the flora of the onmental interpretation of the molluscan as basal part of the Navesink Formation or Mount semblages from this locality as follows: The Laurel Sand in New Jersey. Diagnostic species ranges of living representatives of species from include Holkopollenites sp. C, Casuarinldites the lower Sankaty beds overlap in the area off sp., and Betulaceoipollenites sp. At 133.9 m the Nantucket; the fossil assemblage may in part presence of Brevitricolporites sp. B, Proteacid- represent the transition from a Sangamonian to ites sp. D, and Triatriopollenites sp. B. indicate a Wisconsinan climatic regime; and, the upper correlation with the Wenonah Formation Sankaty beds contain a cold-water molluscan (upper Campanian). Beds equivalent to the assemblage of probable Wisconsinan Age. Pale- Wenonah and Marshalltown Formations are ontological correlation of the Sankaty beds with present at 136.6 m as indicated by the presence the Pleistocene of the Nantucket borehole is of Holkopollenites sp. C and Tricolporites sp. not possible at this time. W. Lower Campanian equivalents of the English- EOCENE town Formation or Woodbury Clay were found Samples from the greensand collected be at 141.5 m. Diagnostic forms are Osculapollis tween 91 m and 98 m yielded sporomorph and aeqiialis Tschudy and Brevitricolporites sp. A. dinoflagellate assemblages. The dinoflagellates The presence of Chomotriletes spp., Complexi- are sparse but well preserved, and include opollis abditus Tschudy, and Retitricolpites sp.
17 A at 173.2 m suggest an age no younger than pites georgensis Brenner, R. vulgaris Pierce, that of the Englishtown Formation, but its age and Tricolporoidites spp., which sugegst equiva is otherwise not definite. lence to the lower or middle part of the Raritan The highest occurrence of Magothy equiva Formation (lower to middle Cenomanian). lents (Santonian or possibly lower Campanian) Samples collected below this point are barren was found at 174.2 m, as shown by the presence of all indigenous fossils. of Trudopollis sp. A, Choanopollenites cf. C. transitus Tschudy, and cf. Holkopollenites sp. POROSITY AND PERMEABILITY A, The occurrnce of Complexiopollis abditus Fourteen undisturbed sand samples were Tschudy and C. sp. B at 211.6 m also indicates analyzed using conventional petroleum industry a Magothy age. techniques for porosity and permeability. All Equivalents of the Woodbridge Clay Member were taken from the Upper Cretaceous section of the middle Raritan Formation (middle Cen- between 137 and 307 m. Samples of sand be omanian) were found from 259.2 m to 338.0 m. tween 350 and 457 m were too unconsolidated Characteristic fossils are Ajatipollis cf. A. to obtained undisturbed samples suitable for tetraedralis (Bolkhovitina) Krutzsch, Atlanto- analyses. pollis spp. and Complexiopollis spp. Porosity was high and averaged 30 percent Thin intervals of marginal marine strata for all samples and varied from 24.5 to 35.9 were also observed in the Woodbridge equiva percent with no obvious trend. Horizontal lents at 309.9 m, 319.7 m, and 321.1 m. Each permeability in 12 samples (2 were unsuitable sample contains a distinct assemblage of for analysis) averaged 162 mD (millidarcys) fragile, agglutinated benthic foraminifers of and varied widely from 10 to 780 mD (table the genera Trochammina and Ammobaculites, 2). accompanied by abundant plant fragments and fish teeth. These beds may represent the equiva DISCUSSION lent of the subsurface Bass River Formation of Fetters (1976) in New Jersey, which was de REGIONAL STRATIGRAPHY posited in a continental shelf environment dur We have attempted in figure 7 to correlate ing the major Cenomanian transgression. biostratigraphic and lithostratigraphic units The oldest datable fossiliferous sample defined in borehole 6001 and the Coskata bore (depth 345 m) contains Ajatipollis cf. A. te hole in Nantucket southwest to Long Island traedralis (Bolkhovitina) Krutzsch, Tricolpol- and New Jersey where the stratigraphic re lenites parvuhis Groot and Penny, Retitricol- lationships, though controversial, have been
TABLE 2. Porosity and permeability analyses [Analysts: Core Laboratories, Inc., Dallas, Tex. ]
Helium - Horizontal Depth porosity permeability Sample No.1 Description (m) (percent) to air (mD) 6001-45-1 (15-25 cm) Gray sand 136.6 26.9 10 6001-50-1 (28-36 cm) ____do _ _ 159.4 32.9 431 6001-58-3 (105 cm) __ _do.___ 185.1 29.1 25 6001-59-1 (70-80 cm) _ _do __ 188.3 28.5 780 6001-60-1 (77-87 cm) __ _do _ 192.6 32.8 (3) 6001-61-1 (68-74 cm) _ _do _ 195.9 24.5 Oil 6001-63-1 (37 cm) __ do__ _ 206.1 32.1 111 6001-67-1 (84-94 cm) White sand 222.3 35.9 74 6001-69-2 (100-113 cm) Gray sand 233.9 24.9 15 6001-71-1 (90-95 cm) White sand 244.3 34.7 42 6001-72-1 (70-80 cm) Gray sand 247.2 26.3 162 6001-73-1 (73-85 cm) ___do____ 254.7 29.8 254 6001-82-1 (85-95 cm) Laminated silt 286.0 32.1 22 6001-87-1 (46-49 cm) Gray sand 306.7 31.6 15
1 Sample number is composed of four parts. First four digits give hole number; next two dig-its, core number; last single digit, ction number; measurement in. parenthesis shows position of sample within section and equals centimeters below top position of that ction. 2 mD = millidarcys. 3 Sample unsuitable for permeability measurement.
18 A B D
ISLAND BEACH FORT HANCOCK 5A and FIRE ISLAND BOREHOLE 6001 COSKATA BOREHOLE NJ-OC-T-I HIGHLANDS BORO 1973 NY-SUF-T-9 NANTUCKET ISLAND Modified from Brown, Miller, Composite Secfion Modified from Brown Miller and Swam (1972) Modified from Perry and others (1975) and Swam (1972)
FIGURE 7. Stratigraphic sections showing regional correlation of the Nantucket boreholes (6001 and Coskata) with other holes drilled in the Atlantic Coastal Plain to the west and south. Assignment of Cretaceous stages follows Sohl and Mello (1970). worked out in considerable detail. We used some boundaries) ; Fetters (1976) and Poag microfossils, megascopic lithologic analysis, and (herein) modified the age boundaries by analyz borehole geophysical logs. Lithostratigraphic ing foraminiferal faunas. Lithostratigraphic boundaries were established by Brown, Miller, boundaries were assigned by Perry and others and Swain (1972) in the Fire Island (Suffolk (1975) in the Fort Hancock 5 A well. Most sedi County, T-9) and Island Beach (Ocean County, mentary materials of Cretaceous age and T-l) boreholes (they used microfossils to date younger in the northern part of the Atlantic
19 Coastal Plain are unconsolidated or at most, be present in a nonfossiliferous facies. Cam- semi-consolidated. Therefore, they are called panian sediments are about 90 m thick at Island sediments rather than sedimentary rocks in this Beach, thin to 25 m at Fort Hancock and Fire discussion. Island, and thicken to a maximum of 80 m at The Pleistocene section in borehole 6001 is Nantucket. In contrast, Santonian and Conia- about twice as thick as that in the other wells, cian sediments are thin at both Island Beach which is not surprising because it is much ( 50 m) and borehole 6001 (~30 m) and are closer to Pleistocene terminal moraines than thicker at Fort Hancock (85 m) and Fire the Island Beach well or Fort Hancock well. Island (~125 m). Turonian strata are 90 to The Pleistocene section thins from 85 m in 125 m thick at Island Beach and Fire Island, borehole 6001 to 44 m in the Coskata borehole. but are only about 10 m thick at Fort Hancock. The Coskata borehole lies north of the axis of About 50 m of Turonian sediments are present the moraine. Probably the thicker section at at Nantucket, but the lower boundary is not borehole 6001 is in part due to erosion of under well defined. Cenomanian sediments are almost lying Tertiary sediments and subsequent fill 75 m thick in the three southern holes, but ing by glacial outwash debris. double that at Nantucket. Upper and lower Tertiary sediments are thin or absent in both boundaries of the Cenomanian at Nantucket, the Fort Hancock and Fire Island wells. At however, are only partly controlled by fossili- Island Beach, a 340-m section comprises Mio ferous samples. Only the Island Beach well con cene, Eocene, and Paleocene sediments. Neither tains an Albian section definitely underlain, Pliocene nor Oligocene materials were identi apparently conformably, by Lower Cretaceous fied. At Nantucket, the Tertiary boundaries are sediments. not well defined. An early Eocene fauna was Lithologic variations along the section ap identified between 91 m and 98 m in borehole pear to reflect mainly the changing relative per 6001; on the basis of these fossils and lithology, centages of sand and clay in the Cretaceous we have assigned a Tertiary age to about 25 m sediments. Upper Quaternary sediments are of the section. In the nearby Coskata borehole, mainly sand and gravel, whereas Tertiary de lower Eocene of approximately equal thickness posits contain more silt and clay. The Upper was identified on the basis of a sparse planktic Cretaceous sediments in the Island Beach well, foraminifer assemblage. This is overlain by a Fort Hancock well, and Nantucket borehole thin (10 m) Pliocene or Miocene section (that 6001 contain more sand and clay at the top and was apparently eroded at the site of the Nan- become clayey toward the middle of the section. tucket borehole), and underlain by almost 30 m Sand again becomes more prevalent during of Paleocene sediment. Our failure to find the early Cenomanian and Albian time. The Fire Paleocene section only 10 km away in borehole Island well, however, appears to have much 6001 may be due to the poor sample recovery in coarser clastic sediments throughout the entire this interval. Upper Cretaceous section than the other three. Thus, the sedimentary facies vary mainly in The Upper Cretaceous section down to the texture finer detritus more common at Island top of the Albian is similar in thickness (300- Beach and Nantucket, but coarser detritus more 400 m) in the Island Beach, Fire Island, and common at Fire Island. Nantucket boreholes. Only at Fort Hancock is A paleoenvironmental evaluation of the fauna the section significantly thinner (about 200 m and flora in the sediments of the wells revealed thick). This appears to be due mostly to ero that during late Tertiary and Quaternary time, sion of the Maastrichtian section at the top of at all locations, sediments were deposited in the Upper Cretaceous strata and to a reduced nonmarine to marginal marine conditions (fig. thickness of Turonian sediment. 8). During the early Tertiary, however, sedi In detail, the Maastrichtian sediments are ments were accumulating in a middle to outer thickest (60 m) in the Island Beach well and shelf environment in all areas. Despite the thin to almost 35 m in the Fire Island well. similarity in facies along the line of section, the They were not identified at Nantucket but may environment of deposition during Late Cre-
20 ISLAND BEACH FIRE ISLAND NANTUCKET USGS 6019 N.J. NY MA. QUATERNARY*
200
400- UPPER \;-:: CRETACEOUS:::: cr 600- LU LU LONG ISLAND PLATFORM o 800 W LOWER < CRETACEOUS I-cr UJ Z IOOOH GEORGES BANK LU Q_ VERTICAL EXAGGERATION = X528 BASIN
1200- EXPLANATION
OPEN MARINE SHELF
1400- MARGINAL MARINE IGNEOUS OR METAMORPHIC ROCK
I600 J
FIGURE 8. Section from New Jersey to Georges Bank along the inner edge of the Continental Shelf showing the environment of deposition of the sediments. See figure 7 for location of wells; USGS borehole 6019 is located and described in Hathaway and others (1976). The interval labeled Quaternary in the Nantucket boreholes contains thin beds of Miocene or Pliocene age which were deposited in marginal marine conditions. Depositional environments shown are based on interpretation of paleontologic evidence. taceous time at Nantucket was significantly is dominant. The only marine interval detected different from that at Island Beach and Fire in the Upper Cretaceous sediments at Nan Island. Both the Island Beach and Fire Island tucket was a marginal marine assemblage of wells contain a Late Cretaceous fauna char agglutinated foraminifers deposited during the acteristic of a shelf environment, whereas at Cenomanian. This apparently reflects the global Nantucket a nonmarine sporomorph assemblage Cenomanian marine transgression, of which
21 Fetters (1976) also found evidence in the (Bothner, 1977). Because of sparse control in Island Beach well (represented by his Bass the area of the anomaly that passes through River Formation). Nantucket, no modeling has been done. How The Fort Hancock well apparently bottomed ever, the basalt cored from 457 to 514 m in Albian sediments; the Fire Island well bot beneath Nantucket may account for the equally tomed in crystalline basement; and the Nan- large anomaly there. Thus, the gravity data tucket borehole 6001 bottomed in Jurassic or depicts two linear positive anomalies that may Triassic volcanic rocks overlain by barren sedi be caused by basalt intruded into crystalline ments inferred to be Albian on the basis of basement beneath Cape Code and Nantucket. tenuous correlations of electric logs. The aeromagnetic survey of the area is based In summary, Upper Cretaceous sediments are on a 3.2 x 32 km line spacing and hence the apparently uniform in thickness along strike coverage is excellent. A northeast grain is evi between Island Beach, N.J., and Nantucket. dent that is roughly parallel to the trend of the Only at Fort Hancock is the section signif two positive gravity anomalies. The magnetic icantly thinner, but within the time strati- trend is characterized by an area of low mag graphic stages, the thickness of sediments does netic gradients that extends between eastern vary significantly, possibly indicating changes Martha's Vineyard and western Nantucket. in sediment supply with time. However, pale- This is flanked on the southeast and northwest ontologic and well control are insufficient to by higher gradients and closely spaced anom rule out the presence of unconformities or alies. A possible interpretation of this contrast faults that also could affect observed thick is that the magnetic basement lies closer to the nesses. Northeast of the Island Beach well, surface on the northwest and southeast than in where Lower Cretaceous sediments were not the area between the islands where it is more positively identified, the updip limit of Lower deeply buried by sediments (Klitgord and Cretaceous sediments apparently lies seaward Behrendt, 1977). Conceivably, the basalt found of the line of section. in the Nantucket borehole is responsible for the REGIONAL STRUCTURE higher gradients at Nantucket, and a similar body or bodies of mafic rocks are responsible Recently acquired shipboard gravity and for the higher gradients to the northwest under aeromagnetic data on the Atlantic continental Cape Cod and Martha's Vineyard. margin have been mapped by Grow and others (1976 and by Klitgord and Behrendt, 1977). Several seismic profiles have been run on the The shipboard gravity coverage in waters sur Continental Shelf, both north and west of Nan rounding Cape Cod, Martha's Vineyard, and tucket. The nearest profile to the west (USGS Nantucket is sparse; however, an ocean bottom seismic line No. 5, CDP) has been interpreted seismic survey of Cape Cod Bay (Bothner, by Grow and Schlee (1976) ; the nearest profile 1977) provided additional coverage north of to the north is an unpublished single channel Cape Cod. Together, these data reveal a large survey conducted by the USGS in 1972. Our (> +30mGal (milligals)) linear positive grav reinterpretation of the multichannel profile is ity anomaly elongated north-northeast that shown in figure 2. We believe that the deeper passes through the eastern part of Martha's high-angle reflectors are rocks of Jurassic and Vineyard and crosses Cape Cod just east of the Triassic age that fill possibly faulted basins Cape Cod Canal (fig. 9). A similar linear similar to those mapped under the Continental feature of approximately the same magnitude Shelf in the Gulf of Maine and beneath Georges (> +30 mGals) lies to the southeast, and, Bank basin (Uchupi, 1970; Weed and others, though control is absent, its axis appears to 1974; Oldale and others, 1974; Ballard and pass through the site of the Nantucket bore Uchupi, 1975; Schlee and others, 1976; Schlee hole 6001. The positive feature passing through and others, 1977), and off Canada (King Martha's Vineyard has been modeled as a large and MacLean, 1975). Though borehole 6001 mafic body intruded into crystalline basement cannot be projected precisely into these pro that probably is buried on Cape Cod and under files, its location probably lies close to the Cape Cod Bay only by Pleistocene glacial drift southeastern margin of an extension under
22 42°00'
4I°00' -
CONTOUR INTERVAL: 10 MILLIGALS 0 10 20 30 40 50KM
40°00' x
70°00 7I°00' 72°00' 73°00' FIGURE 9. Gravity data in the Nantucket region. Two elongated positive anomalies (shaded) pass through the Martha's Vineyard and Nantucket areas, respectively (modified from Grow and others, 1976).
Nantucket Island of the basin shown in the the Jurassic and Triassic basin that projects cross section (fig. 2). north of Martha's Vineyard and Nantucket. We The Jurassic or Triassic basalt penetrated interpret a displacement of these reflectors and may have been injected along a zone of crustal the overlying flat reflectors as evidence of a late weakness associated with flexure or fracture of fault that cuts both the Jurassic and Triassic the basin margin and extruded as flows. The basin and presumed Cretaceous sediments; the strong reflector at the northwest end of the fault may be as young as Tertiary, but prob profile shown in figure 2 may represent such ably does not cut Pleistocene deposits. flows. Thus, partly on the basis of the informa tion from the borehole, we suggest that the HYDROLOGY geophysical data may best be explained by a Jurassic and Triassic basin or graben, with a The water table at borehole 6001 lies at northeast-trending axis, that lies between Nan about 3.7 m above sea level or 7.3 m below the tucket and Martha's Vineyard. top of the hole. To a depth of 158 m, pore water A single channel seismic profile north of Nan salinity was less than 1 ppt (parts per thou tucket (fig. 10) shows steeply dipping and sand). From 158 to 192 m, it increased irreg folded reflectors, which we interpret as part of ularly to 29 ppt; this interval probably repre-
23 28 AUGUST 1972
o o LJ
LJ
Off Great Pt. Great Round Shoal Channel Nantucket Nantucket Sound LJ 0.0 t or I- 0.1
0.2 ii o 0.3
0.4
0.5
0.6
0.7 IOKM IONMI
EXPLANATION Q, Quaternary T, Tertiary K, Cretaceous J, Jurassic ~fc, Triassic Nantucket Is.
LOCATION MAP
FIGURE 10. Single channel seismic reflection profile (R/V F. V. Hunt, USGS, Leg III, August 28, 1972, 0230-0510 hours), east to west through Great Round Shoal Channel and Nantucket Sound (looking south), showing stratigraphic interpretation. We believe that the fault at 0252 cuts both Jurassic- Triassic and Cretaceous sediments. Sediment, filling stream channels is interpreted as Pleistocene in age.
24 n o oa | a^ c-t- DEPTH, IN FEET BELOW LAND SURFACE CD "S 02 05 05 ppt(thatingofseawto33 freshwaterbetweenlibrium benealfreshwaterlensthicka transitionzonthewaterand permeabilitylowsandsand o3 zonediffusiontosentstheof OOOOOOQO salinity,porelens,waterithe I-1 r-h o____o____o____o____o____o____o____o____p Nantucket),againdecreasedt aquifercoastalaseawaterin n'a; comprisesinterbeddedleizone oc-f- I I I I I I I I I I I I I I I I I a4 CD CD o cr A/V/V" To ELECTRICAL n c-f- CD Cf ^* L^C CONDUCTIVITY cr CD P J b s CL e o 05 CD r-h 05 o ! 1^» *^ y"*1 c-f- r-f- CD a 5 \] " "^*"*^ * """> **\f \ / CD rt- CD P O 5' i .- * T I I 1 T / H ui Qa4 CD * ' ' ' I M 1 O cr ? Ms CD o" m-^^ " a4 a a4 CD p 2. as 3 o . p k. am P CO £LP" 05 cT 05 §§' CD a CL t-» ^ surrounding;er o pptlessthan0.5 equi-ydrostatic permeableesof altwaterandis - . Us iteadofincreas- However,below 3 prin-Herzberg Nantucketthat representthus SB- o Oa4 3 CD o CD c c Ms a4 CD CD a p 05 05 a a- CL CD to CD cm l~" MS cr *^ *cs H-thr1
26 distribution of permeability of the Atlantic Coastal M. H., Weed, E. G. A., and Rhodehamel, E. C., 1977, Plain, North Carolina to New York: U.S. Geol. Fresh ground water stored in aquifers under the Survey Prof. Paper 796, 79 p. Continental Shelf; Implications from a deep test, Cushman, J. A., 1904, Notes on the Pleistocene fauna Nantucket Island, Massachusetts: Water Resources of Sankaty Head, Nantucket, Mass.: Am. Geologist, Bull., v. 13, no. 2, p. 373-386. v. 35, p. 169-174. Koteff, Carl, and Cotton, J. E., 1962, Preliminary results 1906, The Pleistocene deposits of Sankaty Head, of recent deep drilling on Cape Cod, Massachusetts: Nantucket, and their fossils: Nantucket Maria Mit- Science, v. 137, no. 3523, p. 34. chell Assoc., pub. 1, no. 1, p. 1-21. Manheim, F. T., 1966, A hydraulic squeezer for obtain Desor, E., 1849, Deposit of drift shells in the cliffs of ing interstitial water from consolidated and uncon- Sancati Island of Nantucket, in a letter to W. C. solidated sediments, U.S. Geol. Survey Prof. Paper Redfield: Am. Assoc. Adv. Sci. Proc., v. 1, p. 100- 550-C, p. C256-C261. 101. Merrill, F. J. H., 1896, Post-Pliocene deposits of San Grim, R. E., 1968, Clay mineralogy: New York, Mc- katy Head [Nantucket, Mass.] : New York Acad. Graw-Hill, 596 p. Sci. Trans., v. 15, p. 10-16. Grow, J. A., Bowin, C. O., Hutchinson, D. R., and Kent, Milliman, J. D., and Emery, K. O., 1968, Sea levels K. M., 1976, Preliminary free-air gravity map during the past 35,000 years: Science, v. 162, no. along the Atlantic continental margin between 3858, p. 1121-1123. Virginia and Georges Bank: U.S. Geol. Survey Minard, J. P., Perry, W. J., Weed, E. G. A., Rhode Misc. Field Studies Map, MF-795. hamel, E. C., Robbins, E. I., and Mixon, R. B., Grow, J. 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